From the look of it, you might think that a starfish has no eyes.
But in fact, it has an eye on the end of each arm. Most starfish
have five arms, so they also have five eyes, but some starfish have
as many as twenty arms (or more), and as many eyes.
The very simple eyes of a starfish are unable to form images. Each
eye is a tiny spot of red pigment that is sensitive to light. Nerves
run from the pigment spots to the starfish's central nerve ring.
The signals from the eyespots affect the animal's behavior, enabling
it to avoid light that is too bright and change its light preferences
according to the time of day, water chemistry, and other factors.
Since a starfish has no brain, it would not be able to make much use
of images, even if its eyes were able to form them.
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Inside Out Stomach
A starfish turns its stomach inside out to eat. When it finds something tasty (like a snail), it extrudes its stomach through a tiny hole. The stomach is like a transparent bag made out of thin rubber. It wraps around the prey, completely surrounding it, and the prey is digested.
If the prey is a tough morsel like a hard-shelled mussel, the starfish attaches its suction-tube feet to the mussel's shells and simply pulls them apart. It can do this because it is able to exert a huge, steady force with a network of hydraulic tubes that run through its entire body. Once the shells are open, the stomach goes in through the gap and dinner is served.
